This invention relates to irrigation, and more particularly to an apparatus and method for a hybrid low volume and sprinkler irrigation system. The invention provides a site selectable arrangement for providing a new, low volume method of irrigation along with a conventional irrigation method, both from a convention sprinkler head installation.
Abroad and in the United States, a large percentage of potable, fresh water consumption is utilized for irrigating landscape and ornamental plantings. The state of the art irrigation systems utilized for delivering this water to landscape plantings are inefficient and contribute greatly to the exhaustion of water reserves in many areas. Sprinkler head systems are most commonly used for landscape purposes. The goal of a sprinkler head system is to evenly distribute the water through the air to a given area at a rate equivalent or less than the hydraulic loading rate or water infiltration rate of the surrounding soil. At this rate, the evenly distributed airborne water droplets fall to the ground and are absorbed into the soil.
However, the tiny spray droplets necessary to achieve uniform water distribution are vulnerable to wind and are more often than not blown out of the area intended to be irrigated, contributing to the over spray problems. Run-off occurs because the sprinkler heads tend to deliver water to an area too quickly for the water to be effectively absorbed into the ground. In addition, water droplets from the sprinkler head systems tend to impinge on surrounding structures such as houses, fences, and vehicles for example, causing discoloration, staining, and other damage. Despite these limitations, sprinkler irrigation systems easily make up the majority of landscape irrigation systems installed today.
Low volume surface drip irrigation devices and lines, typically emitting water in the range of 0.5 to 2 gallons per hour, use an extensive network of conduits. Emitters are attached to the conduits and are spaced apart on the surface of the area to be irrigated. The water drips from these emitters at slow rates and is mainly influenced by capillary action and gravity once the water enters the soil area directly around the emission point. Delivery of water in this manner does eliminate over spray and run-off, but is only practical for landscape plantings in areas not subject to traffic or heavy maintenance. Even in landscapes, surface drip irrigation is not practical for dense plantings with shallow root zones such as ornamental ground covers or turfs. If surface drip irrigation were used in traffic areas, such as lawns, the lines would have to be laid down 12 to 18 inches apart from each other and taken up in between irrigations to allow the lawn to be used and maintained. This impracticality, combined with the detracting visual appearance of the lines placed every 12 to 18 inches along the surface of the lawn, make surface drip irrigation totally unacceptable.
Subsurface drip irrigation systems consist of low volume drip emitter lines, with drip emission rates ranging from 0.5 to 2 gallons per hour. The lines and emitters are placed beneath the soil surface in order to provide watering in the root zone. The lines commonly consist of extruded polyethylene tubes with calibrated emission drip devices either inserted onto or into the tube. The water is emitted at regular intervals along the line buried below the soil surface and is distributed by the effects of capillary action in the soil and gravity. The lines are typically buried 6 to 8 inches below the soil surface and are spaced 12 to 18 inches apart in order to attempt to provide uniform watering to the top soil layers in between and above the drip lines.
However, due to the effects of gravity combined with the capillarity of the soil below the drip lines, more than 50% of the water percolates below the drip line level and is not available to the lawn and shallow rooted plantings. In addition to inefficiencies, these buried lines and emission devices are plagued with problems of plugging due to the ingrowth of plant roots. State of the art solutions to this root ingrowth problem have consisted of using toxic chemicals impregnated within the lines or emission devices or injected into the irrigation water to kill the roots around the emission devices. Even if roots are kept out through chemical treatments, soil may work into the emission devices due to the low velocity and mass flow rate of the water exiting the emission devices and this soil may also plug the devices. The subsurface emitters may also be plugged by insects, insect eggs, and various other natural blocking agents.